Small taps general questions

[Steve HuckinsParticipant @stevehuckins53362]

Morning all.

I am working on the PMResearch no1 and converted most threads to M3 and M2 instead of the American cheese heads supplied in the kit.  I didn’t feel I wanted to go and buy all the necessary taps and dies that would be required according to the drawings. A bit of a mix of imperial and metric throughout the build but I am enjoying the challenge this brings.

I am wondering about the use of plug taps that normally come with a set of 3 taps, eg M3 1st 2nd and plug.  The plug taps rarely seem to give a thread right down to the bottom of a blind hole and where it is necessary for a short amount of thread there seems to be little to play with. An example would be for oil cups where there is a short amount available to thread.  I understand that a bottom tap is a different animal in that it will give a better depth of thread.  Is it advisable to obtain bottom taps alongside plug taps already in the sets of three? Also is a bottom tap really different from a plug tap? Some suppliers use one term or the other. So if I bought a bottom tap would it really be different from a plug tap? Also would it work to grind off the lead in threads of a spare 1st or 2nd tap to use as a bottom tap? Quite a lot of queries here so apologies for rambling.

Steve

[Clive Brown 1Participant @clivebrown1]

I regard commercial “bottom taps” and “plug taps” as one and the same. If I want to tap right to the bottom of a hole, I either (reluctantly) grind the tip off a commercial tap or make one from silver steel.

[noel shelleyParticipant @noelshelley55608]

Take the plug or bottom tap and grind the end or point down to give the effect you want, quite a normal practice ! Good luck Noel.

[JasonBModerator @jasonb]

I also grind the end “point” but not the lead

But rather than buy three taps just get a spiral flute which has a similar lead to a plug tap. It’s all I use these days.

[DellParticipant @dell]

I do the same as JAsonB although because I only restore antique clocks I haven’t been able to find any smaller than M3 and I use down to M1 and BA.

[JasonBModerator @jasonb]

YG-1 go down to M2 though the smallest of theirs I have is M2.5 from Cutwel. My M2 came from Ali and is branded UCAN as the small YG are not cheap.

[HOWARDTParticipant @howardt]

Plug taps still have a lead in the region of two or three threads and have an external centre as well.  It is quite common to grind off the external centre to reduce the lead.  With small sizes if you can drill deeper and use a taper tap to produce the tap hole depth you require, this will reduce the chance of breaking a tap.  Dont over use the taps, as soon as you think they aren’t cutting easily discard and use a new one.  Also ensure the tap is vertical, use a guide to assist and lubricate.  You dont need more than two diameters of thread in a hole, think of how thick a full nut is.  If you find the tapped hole is sloppy, try reducing the tap drill by 0.1, small drills easily cut oversize unless you can run them at the required speeds.

[bernard towersParticipant @bernardtowers37738]

I have quite a lot of plug taps that have all the lead ground off in the ME 32 and 40 rates they are brilliant when making nuts for pipe fittings

[GeorgineerParticipant @georgineer]

I haven’t time to check at present, but memory says that the tap we call a “second” is what the Americans call a “plug”.  If that’s the case (correct me somebody if I’m wrong) it could explain any confusion.

George

 

[Martin KyteParticipant @martinkyte99762]

Just to state the obvious. When attempting to use a tap to thread to full depth in a blind hole do remember to clear all the swarf out of the bottom before the final cut.

 

[JasonBModerator @jasonb]

Snipped from the Dormer threading catalogue.

Most spiral flute taps have the “c” type lead which is a taper over 2 to three times the pitch. makes them less tapered than a plug but not quite as tapered as a bottoming. Other makes also use the same letter codes.

So that M3 spiral flute tap will thread to within 1 to 1.5mm of the full dia bottom of your hole. And no muck in the bottom to stop it going in as far as possible.

For things like oil cups consider a fine pitch much like old UK drawings would have specified ME threads and you will get even closer to the bottom as the pitch is less for the same given diameter

[Georgineer]

On Georgineer Said:

I haven’t time to check at present, but memory says that the tap we call a “second” is what the Americans call a “plug”.  If that’s the case (correct me somebody if I’m wrong) it could explain any confusion.

George

 

A quick google of a .com site says you are correct. US Plugs are UK 2nd taps

[Steve HuckinsParticipant @stevehuckins53362]

Thanks to all for the helpful feedback so far. I will try Jason’s recommendation for spiral flute taps and also grind off spare taps as required. I do use tap guides and good lube as recommended by many on the forums.

Back to the workshop and get to it …….👍

regards Steve

[John PurdyParticipant @johnpurdy78347]

Just to clarify, in Canada (and the USA) taps are listed as Taper, 8-10 thread chamfer, Plug, 3-5 thread chamfer, and Bottoming, 1-11/2 thread chamfer. Smaller ones will have a pointed end and larger ones will be flat with a centre. Like others I regularly grind off the point on the small bottoming taps to be able to tap closer to the bottom of a blind hole where it is shallow.

John

[Howard LewisParticipant @howardlewis46836]

In UK, it is usual for taps to be designated as Taper (or 1st cut), 2nd cut, and the final as a plug (or bottoming) Tap.

I have ground the end off plug taps (or bottoming if you prefer to call them that) to produce threads to the bottom of 5 x 0.5 mm holes.

As Noel says, clean the threads in the hole, and the tap frequently and use lubricant, such as Trefolex or Rocol RTD

Spiral taps are better at clearing swarf from the hole (That’s why the spiral is there)

A clean tooth brush is useful for cleaning Taps after use, especially of white spirit or kerosene is used as well.

Howard

[old martParticipant @oldmart]

Another thing which may help when tapping with small taps at least on flat surfaces is a home made tap guide. Just a little block of any shape with a hole drilled that the tap will pass through to reduce the wobbling which is a danger when handtapping. As already mentioned, if a tap feels wrong, it may be getting blunt and be sure to clear swarf several times as you go. I also grind off any tip cones on plug/bottoming taps, but that means even more caution when finishing a blind hole.

I have made several lathe tools with CCMT06 and DCMT 07 inserts out of Densimet (sintered tungsten alloy), and chose a new tap intended for hard steel and it did not feel right. The Densimet probably would have been better to tap if I had bought a tap intended for aluminium. I found an old tap in amongst the hundreds that we have at the museum which finished the holes much better, you don’t know what may work until you try it.

[Mark RandParticipant @markrand96270]

Yet another bit of elucidation:- The reason smaller taps have a conical end is to hold them in a female centre while grinding them (larger ones often have a conventional centre hole). if you aren’t going to try to sharpen/regrind them (who would in these sizes?) then grind the conical end off. On the plug/bottoming/No3 tap, grind off as much of the lead as you need to get the thread depth you want. It will be threading into a fully formed hole to start with and only needs to clean up the last couple of turns.

Beware of power tapping blind holes with a spiral fluted tap. Even 1/2″ BSW and larger can come to grief if you hit the bottom to hard. DAMHIKT…

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